Minimum pressure relay



Dec 31, 1940 R. c. KlRcHHoFF MINIMUM PRESSURE RELAY Filed Nov. 18, 1939 ATTORNEY.

Patented Dec. 31, 1940 MINIMUM PRESSURE RELAY Richard Carl Kirchhoff, Chicago, Ill., assignor to The Powers Regulator Company, Chicago, Ill., a corporation of Illinois Application November 18, 1939, Serial No. 305'g125 2 claims. (o1. 137-153) My invention relates to a gradually-acting, minimum-pressure relay, particularly adapted The device comprises a casing I Il to which is attached a fitting I I providing three pipe confor the control of pneumatically actuated temnections I2, I3, I4. The connection I2 is inperature or moisture control systems. n tended to supply air from a source under presl An object of the invention is to provide an sure of fteen pounds, this and the other pres 5 instrument by means of which a certain presures mentioned herein being chosen as examdetermined minimum pressure can be mainples. The connection I3 is for a pipe communitained on control apparatus regardless of the cating With a thermostat of the type in whichl action of the thermostat. This is necessary in air under pressure is passed as the temperacertain heating and Ventilating apparatus where ture surrounding the instrument exceeds that of l0 intake or proportioning dampers are operated the setting of the instrument. The connection by air through the iniluence of a thermostat, it I4 isvfor a pipe extending to a damper or other being required that during normal operation control apparatus. such dampers shall not be entirely closed, re- The connection I2 communicates with a pasgardless of the temperature. For example, in sage I5 in the casing. The connection I 4 is to l5 the class rooms of schools it is a requirement in a passage I6 andthe connection IZ is through many jurisdictions that a certain specified minia coiled pipe Il to a passage I8 in a face plate I9. mum volume of fresh air shall be introduced at The casing and the face plate are separated all times. Thus by providing a relay of the charas shown and held in spaced relation by means 2o acter herein disclosed between the thermostat of screws 20, three of which are arranged around 20 and the damper, a certain minimum pressure the periphery of the face plate, the screws enmay be delivered at all times in order to maingaging in sleeves 2I that are in turn held by tain the damper in its minimi-1m Open position. screws 22 extending through the rim of the cas- A relay of the character described should have ing. By turning the screws 20, the spacing of 2.3 certain characteristics, an important one bng the :face plate relative to the casing may be that it shall deliver its minimum specied preschangei sure regardless of the delivery to the instrument Air under pressure admitted through the con- 0f any D1` eSS111` f10 m the thermostat 0f IESS than nection I2 and the passage I5 is controlled by a o the Specled minimum; m 9ther Words that valve 23 normally held against its seat by a spring 0 the relay Shall not Cumulajte lts mmlmum Pres' 24,' the valve having an axial extension 25 in abut- 30 Sure W1th any Pfesme dehvered by the thermo ting relation with the head 26 of an exhaust stat. It 1s essential also that as the pressure Valve 2| A light spring 27a tends to uns-eat from @he Phermostabullds up beyond the mm1' theexhaust valve. The exhaust valve.is part of mum 1t W1H-operate m the Sam? manner as any an assembly carried by a diaphragm 28, the

3o relay that did not possess the minimum pressure periphery of which is held agaist the rim of 35 characienslqs .1l t h the casing by screws 29. The assembly includes For slmphclty the Instrument l us.rated erem a sleeve over which is mounted a stii coiled 1s shown as of constant ratio. It will be undersprmg 3l. The spring at 1ts outer end bears stood, however, that the same principle may be c applied to variable ratio instruments with equal aga'mst the plate of a second dlaphragm 32 the 4o f sleeve 30- being normally out of engagement with acillty. Further, 1t Will be understood that no h The attempt has been made to illustrate any accuthe plate of sajld last named dlap mgm' rate actual position of the various valves or other dlaphragm 32 1s held by means of screws 33 at parts of the instrument; this for the reason that the penphery of the face; plate I9 and a button the movements of the parts are very slight even i :t tlen; atkg dallglglplo; 45

from one extreme to the other and the valves ap e 0 p are of such small size that illustrations of actual the fae Platepositions would be practically impossib1e- It will be noted that the space 35- enclosed by The invention will be more readily understood t"he dlaphragm 32 1S 1n COmInumcation, through by reference to the accompanying drawing; in the duct I8 and pipe I7, Wl'h the thelmOStat, 50 which, while the space 36 is, through the duct I6 and Fig. 1 is a `face view of an instrument such connection I4, in COmmllnCatiOYl With the C011- as contemplated herein; and, c trol apparatus.

Fig. 2 is a sectional view on the line 2-2 of In case a variable ratio instrument is re- Fig 1l quired, the effective diameter of the diaphragm 55 the spring 3l to deflect the diaphragm 28 to the extent of closing the exhaust valve 21 and slightly opening the intake inlet valve 23. The instrument will continue to deliver pressure of four pounds so long as there is a supply of air under pressure. Of course, when it is desired to shut down the system at night or at other times, mere shutting off of the air supply and exhausting the pressure in the system will result in complete closing of the dampers that had theretofore been maintained in at least a partially open position.

Assuming that the control thermostat is set for 35 degrees, no air will be passed from that instrument to the chamber 35 until the temperature exceeds 35 degrees. Thereafter as the temperature rises additional air will be delivered to the chamber 35 and up to four pounds pressure no change will take place in the delivery of air by the instrument to the control apparatus; this for the reason that four pounds of pressure 'is likewise being exerted against the diaphragm 28. However, as the pressure from the thermostat rises above four pounds, the diaphragm 32 will be moved inwardly compressing the spring 3| and exerting pressure against diaphragm 28 tending to bring about a slightly greater opening of the inlet valve 23 to an extent that pressure will be admitted to exactly balance that exerted against the diaphragm 32. This will continue up to the full pressure available and on the reduction of pressure delivered by the thermostat a corresponding reduction will occur in the control line; this for the reason that whenever the pressure exerted against the diaphragm 28 exceeds that exerted against the diaphragm 32, the spring 3| will be compressed, thus permitting an exhaust of air to bring about equalization. When the pressure delivered from the thermostat reaches four pounds, the diaphragm 32 will remain in a fixed position with the button 34 against the face plate and regardless of further reduction in thermostat pressure the instrument will continue to deliver four pounds to the control apparatus.

The form of the heat sensitive element and of the damper control means is of no importance herein and such parts are not illustrated. The

description is predicated on the use of a so-called direct-acting thermostat; that is, one that passes air on an increase in temperature. It will be understood however, that a reverse acting thermostat may be used with a reversal of the action of the relay. Also, that the described instrument is adapted for use in systems in which it is desired to limit damper positions in hot as well as cold weather.

I claim:

1. In a relay of the class described, the combination of a casing providing two inlets and an outlet, one inlet providing for a supply of air at a substantially constant pressure, a valve for controlling the inlet of said constant supply of air, a diaphragm supported on said casing and enclosing a space in communication through said outlet with control apparatus, an exhaust valve carried by the diaphragm in thrust engagement with said inlet valve, a face plate supported on and spaced from said casing, a second diaphragm carried by the face plate and enclosing a space, a flexible pipe connecting said space to said second inlet, a spring between said diaphragms tending to spread apart the same and to maintain the exhaust valve in closed position and the inlet valve in a predetermined open position in the absence of pressure behind said secondi diaphragm, and screw means adapted to adjust the position of the face plate relative to the casing and consequently the compression of the spring between said diaphragms.

2. In a relay of the class described, the combination of a casing providing two inlets and an outlet, on-e inlet providing for a supply of air at a substantially constant pressure, a valve for controlling the inlet of said constant supply of air, a diaphragm supported on said casing and enclosing a space in communication through said outlet with control apparatus, an exhaust valve carried by the diaphragm in thrust engagement with said inlet valve, a face plate supported on and spaced from said casing, a second diaphragm carried by the face plate and enclosing a'space, a iiexible pipe connecting said space to said second inlet, a spring between said diaphragms tending to spread apart the same and to maintain the exhaust valve in closed position and the inlet valve in a predetermined open position in the absence of pressure behind said second diaphragm, and screw means acting on the spring between said diaphragme whereby to vary the compression thereof and consequently the degree of fixed opening of the inlet valve.

RICHARD CARL KIRCHTIOFF. 

